Java Type vs PostgreSQL Type (二) 字元型別之對應

char and Character:
測試Java Types: char and Character 時，首先在PostgreSQL建置資料表
資料表語法:
CREATE TABLE chartype
(
"char" "char",
char1 "char",
id serial NOT NULL,
CONSTRAINT chartype_pkey PRIMARY KEY (id)
)

程式原始碼:
JavaCharTypes:

package zasax.type.chartypes;

import java.io.IOException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.PreparedStatement;
import java.util.logging.Level;
import java.util.logging.Logger;
import zasax.conn.PostgreConnection;

/**
*
* @author YiCheng, Hsiao
*/
public class JavaCharType {

private Connection conn;
private PreparedStatement pstmt;
private ResultSet rs;
private String setSQL = "Insert into chartype (char,char1) values (?,?)";
private String getSQL = "Select * from chartype";

public static void main(String[] args) {
char ch1 = '1';
Character ch2 = new Character('1');
JavaCharType jct = new JavaCharType();
jct.setCharValue('a', 'b');
ResultSet rs = jct.getCharValue();
try {
while (rs.next()) {
ch1 = rs.getString("char").charAt(0);
ch2 = rs.getString("char1").charAt(0);
System.out.println(ch1 + " " + ch2);
}
} catch (SQLException ex) {
Logger.getLogger(JavaCharType.class.getName()).log(Level.SEVERE, null, ex);
}
}
public void setCharValue(char ch1, Character ch2) {
PostgreConnection pc = new PostgreConnection();
try {
this.conn = pc.getConnection();
this.pstmt = conn.prepareStatement(setSQL);
pstmt.setString(1, String.valueOf(ch1));
pstmt.setString(2, String.valueOf(ch2));
pstmt.execute();
pstmt.close();
conn.close();
} catch (IOException ex) {
Logger.getLogger(JavaCharType.class.getName()).log(Level.SEVERE, null, ex);
} catch (ClassNotFoundException ex) {
Logger.getLogger(JavaCharType.class.getName()).log(Level.SEVERE, null, ex);
} catch (SQLException ex) {
Logger.getLogger(JavaCharType.class.getName()).log(Level.SEVERE, null, ex);
}
}
public ResultSet getCharValue() {
PostgreConnection pc = new PostgreConnection();
try {
this.conn = pc.getConnection();
this.pstmt = conn.prepareStatement(getSQL);
this.rs = pstmt.executeQuery();
} catch (IOException ex) {
Logger.getLogger(JavaCharType.class.getName()).log(Level.SEVERE, null, ex);
} catch (ClassNotFoundException ex) {
Logger.getLogger(JavaCharType.class.getName()).log(Level.SEVERE, null, ex);
} catch (SQLException ex) {
Logger.getLogger(JavaCharType.class.getName()).log(Level.SEVERE, null, ex);
}
return rs;
}
}

實際測試程序:

儲存Character值的方式:
在java.sql.PreparedStatement裡，並無存入字元的方法，所以要存取字元值，
得在存取之前將字元值，透過String.valueOf(char ch)的方法轉為字串，再透過
setString()將字串儲存到資料庫。

讀取字元值的方式:
經getBooleanValue()的方法，先透過executeQuery()，
將SQL語法"select * from chartypes"傳入資料庫查詢，回傳ResultSet指派
給rs，再將rs回傳指派給main()區塊的ResultSet，而ResultSet保存著SQL
查詢完後的資料表內容，再分別透過ResultSet將值傳回給char ch1，以及
Character ch2，最後在印出結果a,b，為了確定印出值為資料庫所傳回的，
在初始值上，將char ch1 = '1' ， Character ch2 = new Character('1')，以作
為驗證其結果。而由於ResultSet並無讀取字元值的方法，所以得先透過讀
取字串再利用charAt(0)將回傳第一個字元，所以若要進行字元進出資料庫
的處理，得先轉型為字串，才得以進出資料庫。

整理表格如下:

Java Types	PostgreSQL Types	特性
String(char , Character)	character(n)	長度固定的不可變字元陣列
	character varying(n)	長度固定的可變字元陣列
	text	長度無限制的可變字元陣列